Bendamustine free base is represented by the following structural formula (I)

Bendamustine is used in the treatment of a number of cancers including leukemias, Hodgkins disease and multiple myelomas. Bendamustine is the active ingredient of the commercial product TreandaTM, a lyophilized powder for reconstitution.
Bendamustine exhibits rapid degradation upon reconstitution of the lyophilized product. Bendamustine undergoes hydrolysis by direct substitution rather than an addition elimination process due to the presence of the highly labile aliphatic chlorine atoms. Some of the main degradants of bendamustine are the monohydroxy compound known as HP1 (hydrolysis product 1) and dihydroxy compound HP2 (hydrolysis product 2). The monohydroxy compound appears as the main impurity at Relative Retention Time (RRT) 0.6 and the dihydroxy compound appears as the main impurity at RRT 0.27. Minor peaks appear at RRT 1.2, which are presently unknown.
The stability of bendamustine in water is measured in hours, and is therefore, not suitable for long-term storage in liquid form. The lyophile possesses good chemical stability. However, reconstitution of the lyophile is clinically inconvenient, taking 15-30 mins with implications of chemical instability. There is a need for ready to use (RTU) bendamustine formulations having enhanced stability.